Thought I best check-in and update this.
Over the last few months the cars been in normal weekend use but during that time I’ve been getting bored of the boost, so I have been looking as upgrading the supercharger. The M65 that I fitted is pretty much at capacity on these engines and the supporting pulley mods don’t tend to bring much more to the table, with this in mine I began to hunt down bigger units to fabricate up onto the engine.
At first I saw a few Jag offerings but these would be too large, then I was offered an AMG unit for a silly cheap price but again they are a bit big for the 1.8 BP motor. I did find a rare IHI screw unit from a JDM Mazda Xedos but the nose bearing were shot and these cost more than the Supercharger itself, it was at this point I decided to go down the turbo route.
Now picking a turbo for a MX5 engine is easy, everyone picks the TD04 from a Impreza but I am not everyone. I wanted to start off with something that could offer more ChooChoo” than the M65 but would also open up future upgrades, so after some hunting and investigation I selected a T25 from a late Gen Saab. These are very cheap turbos and usually come with all the Banjo fittings and on the BP they are capable of propelling it over the 220BHP ATW, which is more than enough……For now.
Now fitting a turbo to an MX is no new thing, but fitting one to an MX engine that in a 70s BL car does open up some issues. For speed of install I wanted to just get “Off the shelf” components and bolt it right on after-all the supporting mods (ECU, Injectors, Fuel rail, Fuel Pump ect) are already in place so a map change and we are off. Things are never this easy, the aftermarket pre-made manifolds just wont work due to the inner arches being close and I am not prepared to cut these due to the current regs, so I needed to lend my hand to making a manifold……..
At first I attempted to TIG up a fully stainless system with about as equal length feeds as possible, but regardless of orientation it just would not fit. The turbo needs to be as close to the block as possible for the bonnet/exhaust components to close/fit. This means a log type manifold is the only way forward, as much as there are downsides this is never going to be a Pro-Mod.